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Cation biogeo chemistry

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Information about Cation biogeo chemistry
Education

Published on January 22, 2008

Author: Carmela

Source: authorstream.com

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Cation biogeochemistry of forest ecosystems:  Cation biogeochemistry of forest ecosystems IB 516 6 April 2005 Outline:  Outline conceptual model of cation cycling in forest ecosystems cation sources soil cation exchange patterns of inputs and outputs at HBEF Ca depletion and forest health Al biogeochemistry Terminology:  Terminology base cations (Ca2+, Mg2+, Na+, K+) called base because largely derived from weathering of metal oxide minerals CaO + 2H+ = Ca2+ + H2O reaction consumes protons acid cations (Aln+, Fen+) called acid cations because reactions may produce protons Al3+ + H2O = Al(OH) + H+ actually amphoteric (can act as either acid or base) Slide4:  Conceptual model of cation cycling in forest ecosystems litter soil organic matter leaching loss tree biomass uptake mineralization soil solution atmospheric deposition exchangeable primary and secondary minerals dissolution precipitation Plant available Slide5:  Ca biogeochemical cycle at HBEF From: Likens et al (1998) Slide6:  soil solution atmospheric deposition primary and secondary minerals dissolution precipitation Cation sources Cation sources:  Cation sources weathering chemical and physical disintegration of primary and secondary minerals primary minerals generally formed at elevated temperature and pressure and are unchanged from original igneous, metamorphic, or sedimentary rocks secondary minerals formed from weathering of primary minerals and from precipitation reactions atmospheric deposition generally minor relative to weathering can be important in base-poor ecosystems (e.g., rock composition almost all quartz) Weathering of primary minerals:  Examples of primary mineral weathering are: NaAlSi3O8(s) + H+ + 9/2 H2O →Na+ + 2H4SiO4 + 1/2 Al2Si22O5(OH)4(s) (albite) (kaolinite) CaCO3(s) + H2CO3 → Ca2+ + 2HCO3- + H2O (calcite) CaAl2Si2O8 + 8CH3COOH → 8CH3COO- + 2Al3+ + Ca2+ + 4H4SiO4 (anorthite) weathering rates dependent on parent material, age, soil moisture, temperature, acidity, biological activity driven by production of carbonic and organic acids weathering reactions involve consumption or production of protons Weathering of primary minerals Slide9:  Precipitation Ca concentration and Ca deposition in U.S. From: Likens et al. (1998) Slide10:  soil solution exchangeable Soil cation exchange reactions Soil cation exchange:  Soil cation exchange surfaces of soil particles can have net negative charge two types of surface charge: permanent largely associated with isomorphic substitution in clay lattice substitution of cation with lower charge for cation with higher charge creates net negative charge on clay particle pH dependent charge functional groups associated with soil organic matter RCOOH(s) = RCOO(s)- + H+ OH functional groups on oxide minerals (e.g. Al(OH)3, Fe(OH)3, SiO2) zero point of charge (ZPC): pH at which particle has no net charge pH > ZPC then particle has negative charge pH < ZPC then particle has positive charge Cation exchange:  Multivalent cations are generally retained over monovalent cations (but there are notable exceptions) Al3+ > H+ > Ca2+ > Mg2+ > K+ > NH4+ > Na+. The total quantity of exchange sites on soil is called cation exchange capacity (CEC). CEC can range from 10 mmol(+)/kg for coarse textured soils to 500-600 mmol(+)/kg for fine textured soils with large amounts of clays and organic matter. Cation exchange sites may be occupied by basic cations or acidic cations. This is expressed as: equivalence of basic cations on exchange % base saturation = cation exchange capacity The % base saturation of the soil decreases with decreasing pH. Cation exchange Slide13:  CEC related to soil C and pH From: Johnson et al. (2000) Slide15:  litter soil organic matter tree biomass uptake mineralization soil solution Plant uptake, litterfall, mineralization loop Slide16:  Biologically mediated cation transfers Macronutrients: K, Ca, Mg K: Important in enzyme activation and osmotic regulation. Essential in photosynthesis and starch formation. Mg-Component of chlorophyll. Ca -Plant structural component, used in phosphorylation Micronutrients: Fe, Mn, Zn, Cu, Co, Ni Fe -Chlorophyll synthesis, oxidation-reduction in respiration, constituent of some enzymes and proteins. Plants assimilate nutrient cations. These cations are returned to soil via canopy leaching, litterfall and root litter. Organic matter containing mineral cations is mineralized releasing these elements to the soil solution. Slide17:  Seasonal patterns of Ca in inputs and outputs at HBEF From: Likens et al. (1998) Slide18:  Long-term patterns in input and output of Ca at HBEF From: Likens et al. (1998) Slide19:  Anion leaching drives base cation loss From: Likens et al. (1998) Important gaps in our understanding of cation biogeochemistry:  Important gaps in our understanding of cation biogeochemistry role of mycorrhizae in cation uptake few estimates of mineralization rates how to quantify weathering rates? Slide21:  Ca depletion via acidic deposition can affect ecosystem health From: DeHayes et al. (1999) Slide22:  Growth of sugar maple seedlings enhanced by Ca addition From: Kobe et al. (2002) Slide23:  Mortality of sugar maple seedlings increases after Al addition From: Kobe et al. (2002) Slide24:  Sugar maple decline may be linked to Ca depletion at HBEF From: Likens et al. (1998) Experimental Addition of Calcium to Watershed 1:  Experimental Addition of Calcium to Watershed 1 Material Wollastonite CaSiO3 + H2O + 2H+ = Ca2+ + H4SiO4 Median particle diameter 9.6 µm Chemical composition 87Sr/86Sr = 0.70554 Ca/Sr (g/g) = 1190 Dose % BS 10% 19% theoretical actual 30.2 ton 45 ton Application W1 11.8 ha helicopter 1 ton bucket pelletized 1.5-4 mm water soluble binder Slide28:  Wollastonite pellets on forest floor Slide31:  Sugar maple seedling abundance increases following Ca addition Winter Injury of All Crown Classes of Red Spruce:  % winter injury of current-year red spruce foliage * P<0.05 Hawley et al., UVM Winter Injury of All Crown Classes of Red Spruce Slide33:  Ca as a master variable influencing ecosystem structure and function From: Likens et al (1998) Al biogeochemistry:  Al biogeochemistry Al not a plant nutrient can be toxic to plants and aquatic biota solubility increases with decreasing pH below ~ 5.5 dissolved Al: inorganic (Al3+, Al-OH species, Al-F complexes) organic: complexed with organic acids Slide38:  From: MacAvoy & Bulger (1995)

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